1. Technical Field
The present invention relates to a resilient electrical contact element, or spring contact for making pressure contacts between electrical components, and more particularly to spring contacts and a structure for attachment of the spring contacts to a substrate to form a probe card for use in probing to test integrated circuits (ICs) on a wafer.
2. Related Art
Resilient contact elements, or spring contacts are manufactured in a variety of forms. One type of spring contacts used for probing ICs on a wafer is described in U.S. Pat. No. 5,476,211 entitled “Method of Manufacturing Electrical Contacts, Using a Sacrificial Member” and its counterpart divisional patents, U.S. Pat. Nos. 5,852,871, and 6,049,976, all by Khandros. These patents disclose methods for making resilient interconnection elements by mounting a flexible elongate core element (e.g., wire “stem” or “skeleton”) to a terminal on an electronic component and coating the flexible core element with a “shell” of one or more materials to ensure the resilient nature of resulting spring contacts. Exemplary materials for the core element include gold. Exemplary materials for the resilient coating include nickel and its alloys. The resulting spring contact element is used to make pressure connections between two or more electronic components including between a probe card and integrated circuits on a wafer.
Connection of the spring contacts to a substrate to form a probe card, or other structure with spring contacts is described in U.S. Pat. No. 5,974,662, entitled “method of Planarizing Tips of Probe Elements of a Probe Card Assembly” by Eldridge, Grube, Khandros and Mathieu. This patent describes a probe card assembly, including a substrate with elongate resilient spring contact elements mounted to form a “space transformer.” A space transformer is a multilayer interconnection substrate having terminals disposed at a first pitch, or spacing between terminals, on a one surface and having corresponding terminals disposed at a second pitch on an opposite surface. Space transformation is provided by routing lines in the layers of the substrate used to effect “pitch-spreading” from the first pitch to the second pitch. In use, the free ends (tips) of the elongate spring contact elements make pressure connections with corresponding terminals on an electronic component being probed or tested.
Another type of spring contact elements is described in U.S. Pat. No. 6,482,013, entitled “Microelectronic Spring Contact Element and Electronic Component Having A Plurality Of Spring Contact Elements” by Eldridge, Grube, Khandros and Mathieu, incorporated herein by reference. This patent describes photo lithographic rather than mechanical techniques to fabricate resilient contact elements. As with the mechanically formed contact elements, the resilient contact elements formed using lithographic techniques include a resilient material, such as nickel and its alloys. To manufacture a probe card, or other substrate with resilient contacts using photolithographic techniques, the spring contacts are formed on metal interconnect pads on the surface of the substrate by a series of steps including plating or deposition of material, applying photoresist, masking using photolithographic techniques, and etching. For a space transformer, the interconnect pads on which the resilient contacts are formed connect the resilient contacts to routing lines within the space transformer substrate. Using photographic techniques, close tolerances can be realized to assure alignment of the spring contacts formed thereon with corresponding contact pads on an integrated circuit being tested.